What is the primary cause of cervical insufficiency?

Cervical insufficiency is primarily defined by painless cervical dilation that occurs in the second trimester or early third trimester of pregnancy, often leading to preterm birth or miscarriage. The condition is characterized by the inability of the cervix to maintain a pregnancy due to structural or functional abnormalities, which can lead to a premature opening of the cervix without accompanying pain or contractions.

In this context, the absence of pain makes option A the most accurate representation of cervical insufficiency. The lack of painful contractions or other signs often distinguishes cervical insufficiency from other obstetric complications. Other factors, such as infection, can contribute to adverse pregnancy outcomes, but they are not the primary cause of cervical insufficiency specifically. Thus, the correct answer highlights the key feature of this condition, which is the painless nature of the cervical dilation.